Indirect imaging of the magnetic reconnection region in flares using observations of chromospheric ribbon structure
Solar flare reconnection is widely understood to occur in a thin region near the current sheet where (roughly) oppositely oriented magnetic fields meet. This process is generally neither uniform nor steady state, and the resulting structure may be the result of instabilities, such as tearing-mode or Kelvin-Helmholtz, in the reconnection layer. Direct observations of flare current sheets are rare, one famous example being the 2017-Sep-10 X-flare. This scarcity presents significant challenges to investigating fundamental reconnection mechanisms. Flare ribbons, on the other hand, are easily observed and identified in imaging and spectroscopic flare observations. It is generally understood that flare ribbons represent the chromospheric footpoints of freshly reconnected field lines. The direct link between the reconnection region and the flare ribbons via the magnetic field lines suggests that flare ribbons may be used as an observational proxy for the structure and evolution of the reconnection region. Imaging and spectroscopic observations of flare ribbon substructure have previously been used to identify instabilities in the reconnection region. These results strongly suggest that the large- and small-scale structuring of flare ribbons represents an "image" of the coronal reconnection region, projected onto the denser plasma of the chromosphere. This image is of course distorted by the magnetic field geometry, similar to a funhouse mirror. The central science objective of this proposal is to invert this process, "de-projecting" the ribbon images to obtain indirect images of the evolving reconnection region. From this, we aim to measure the spatial and temporal scales of instabilities in the reconnection region in their full 3-D environment.